(a) Field of the Invention
The present invention relates to an apparatus for symbol timing detection for a wireless communication system. More specifically, the present invention relates to an apparatus for symbol timing detection for a wireless communication system that is for detecting a start of actual user data that is communicated.
(b) Description of the Related Art
For data transmission in frame units in a wireless communication system, a transmitter transmits signals of a predefined type to a receiver. A signal of this type is called a preamble or training signal, of which an interval supports several functions concerning the determination of the presence of an effective received signal, automatic gain control, initial carrier frequency error estimation and compensation, symbol timing detection for determining the start of actual user data, etc.
At the receiver of the wireless communication system, a symbol timing detector performs a function of detecting the start of the actual user data. The symbol timing detection methods concerned include an autocorrelation method and a crosscorrelation method.
U.S. Pat. No. 6,563,856 (May 13, 2003; Frame Synchronization and Detection Technique for Digital Receiver) proposes a technique for acquiring synchronization of digital receiver frames using a characteristic signal called a frame marker, and it uses the cross-correlation method. The crosscorrelation method involves a large number of calculations every clock period, and causes a deterioration of performance in the case of occurrence of a carrier frequency error.
Contrarily, the autocorrelation method involves a lesser number of calculations and is simply realized.
FIG. 1 is a schematic of a frame having a preamble of a cyclic signal type for wireless data communication in frame units.
Referring to FIG. 1, the preamble of the frame is cyclically repeated with a cycle T. FIG. 1 shows a preamble of which the cycle T repeats ten times, with a waveform including 16 samples per cycle.
The general packet-based wireless data communication system uses signals of the same type as the preamble to perform schematic estimation and compensation of carrier frequency errors and symbol timing detection for detecting the accurate start of the frame.
FIG. 2 is a block diagram of a conventional apparatus for symbol timing detection using the autocorrelation method.
The conventional apparatus for symbol timing detection using the autocorrelation method comprises, as shown in FIG. 2, a delay section 201, a complex conjugate processor 202, a multiplier 203, a moving average calculator 204, a squarer 205, a moving average calculator 206, a normalizer 207, and an absolute value processor 208.
The delay section 201 delays a received signal by the correlation delay sample value Δac of the received signal, and the complex conjugate processor 202 multiplies the complex conjugate rk※ of the delayed signal by the received signal.
The multiplier 203 multiplies the signal of the complex conjugate processor 202 by the original received signal to output a value qk, and the moving average calculator 204 stores the output signal qk of the multiplier 203 in a shift register having a window size of Wac and calculates an average of the stored values to output a value xk.
The squarer 205 makes the second power of the magnitude of the received signal, i.e., sk=|rk|2, and the moving average calculator 206 calculates the moving average yk of the squared magnitude of the received signal.
The normalizer 207 divides xk by yk to detect a normalized correlation value, and the absolute value processor 208 searches for the maximum value based on the calculated value ρk to estimate the symbol timing according to the result ρk.
The detection of timing synchronization using the cyclically repeating preamble structure and the autocorrelation method is dependent upon the selected values Δac and Wac in regard to its performance and complexity of implementation. In addition, the leading part of the preamble of FIG. 1 has an interval that determines an adequate level of the received signal by an automatic gain control. There is thus a problem that the signals after the analog-to-digital converter may be inaccurate in that interval due to saturation of the signal level during the operation of the analog-to-digital converter.
The use of the value Wac that is for averaging a large amount of data is desirable, since the size of the moving average window has an influence on the reliability of the correlation signals. However, there is a need for considering the relationship between the performance according to Wac and the complexity of implementation.